when i said the design was efficient, I will show you what i mean. some ppl might be surprised by the internal design of a heatercore. AFAIK, purpose built ones dont have the design like this. atleast not these little fins that increase surface area (not frontal) by orders of magnitude. anyway here is the pic. BTW, i hijacked this from WEAPON over at XS. I think he is a member here too..
In the pic the red arrows poitn to the water chanels (the thing slits) and the blue arrows point to the flow chanels for the air. notice the little fins (actually litte slats cut into the copper) that cover the air chanels.. those guys increase the exposed surface area quite a bit compared to having the channels smooth.
